October 2, 2012

Sea Rise Will Be Irreversible Over Next Several Thousand Years Due To Greenhouse Gas Emissions

A groundbreaking study by a team of European researchers warns that greenhouse gas emissions will cause an irreversible rise in sea level over the next several thousand years.

The study, published in the latest edition of the journal Environmental Research Letters, expanded the scope of typical climate change studies to include thousands of years in its projections and also took into consideration all of the Earth´s land ice, something which had never been done before.

Using thermomechanical models and a global glacial melt algorithm, the researchers analyzed four different scenarios outlined by the Special Report on Emissions Scenarios (SRES) and one additional scenario.

They found that previous and current carbon emissions have already committed to raising sea levels by 3.6 feet by the year 3000 and the predicament could get worse.

If climate change impacts are analyzed under an A2 SRES scenario that is defined by divided but expanding global populations, the sea levels could rise over 23 feet over that same time period. SRES scenarios defined by a more united and integrated world were found to project smaller changes, around 6 to 10 feet of increased sea levels, highlighting the need for a coordinated global plan for reducing emissions.

"Ice sheets are very slow components in the climate system; they respond on time scales of thousands of years," co-author Philippe Huybrechts, a climatologist at Vrije Universiteit Brussel explained.

"Together with the long life-time of greenhouse gases in the atmosphere, this inertia is the real poison on the climate system: anything we do now that changes the forcing in the climate system will necessarily have long consequences for the ice sheets and sea level."

All of the scenarios analyzed by the researchers showed that Greenland´s ice sheet was responsible for over half of the sea level rises. The thermal expansion of the oceans was the second highest contributor to projected sea level increases.

The long-term impacts of greenhouse gas emissions are the result of their longevity in the atmosphere and the long-term response inherent in the ocean and the ice sheets, according to the report.

"Ultimately the current polar ice sheets store about 65 metres (213 feet) of equivalent sea level and if climatic warming will be severe and long-lasting all ice will eventually melt,” Huybrechts said.

"Mankind should limit the concentration of greenhouse gases at the lowest possible level as soon as possible,” he added. “The only realistic option is a drastic reduction of the emissions. The lower the ultimate warming will be, the less severe the ultimate consequences will be."

The scientists added that they believe this is the first study to include glaciers, ice caps, the Greenland and Antarctic ice sheets and the thermal expansion into sea-level projections. They also admitted that their models are subject to uncertainties in climate sensitivity, but that their model was designed with low sensitivity in mind.

The model also included the average physical parameters for polar ice sheets that are not typically used in climate projections due to computational constraints. Many climatologists find it challenging in accounting for the 200,000 glaciers around the world in a variety of climatic settings.